User Story 8: Start and manage Pomodoro timer

[Pur3-MAlice]

As a user, I want to be able to start a Pomodoro timer for focused work sessions, with configurable work and break intervals.

[Pur3-MAlice]

User Story 8 Tasks:

• [x] Task 4.1: Create a UI for starting and managing Pomodoro sessions.
• [x] Task 4.2: Implement the Pomodoro timer logic.